As is well known, NMR systems have been in use for many years and can be used to provide imaging and/or analysis of a sample being tested. Various different types of NMR are known, including “high-field” NMR that uses relatively high frequency magnetic fields and high static magnetic field strengths, and “low-field” NMR that uses relatively low frequency magnetic fields and low static magnetic field strengths. Typically, low-field NMR systems are comprised of products and devices designed for applications utilizing a single detection channel, and high-field NMR systems are comprised of products and devices designed for applications utilizing single or multiple detection channels. Examples of existing low-field NMR detection products and devices include a single channel Earth's field groundwater detection device, such as described in U.S. Pat. No. 3,019,383, and a single channel commercial groundwater detection products “Numis” and “Hydroscope” which are derived from the design such as described in U.S. Pat. No. 3,019,383. Various multi-channel NMR detection devices have been designed for high-field NMR applications.
A number of specific hardware designs have been developed to simultaneously optimize the NMR signal to noise ratio and minimize mutual coupling between adjacent coils in a multiple coil NMR receive array. In particular, in the field of medical magnetic resonance imaging (MRI), the following general approaches to this problem have been developed, some in combination with one another: a) the use of transmission line segments of length equal to an integer multiple of a quarter wavelength at the RF operating frequency, in conjunction with series crossed diodes between the transmitter and the transmit coil(s), to isolate noise from the transmitter during the receive operation, such as described in U.S. Pat. No. 4,739,271; b) the use of a pre-damp circuit, which includes a low input impedance pre-amplifier transformed through a quarter-wavelength transmission line segment to achieve a high input impedance to the coil, thereby reducing currents on the coil during receive mode, and hence reducing coupling between adjacent coils during receive mode, such as described in U.S. Pat. No. 4,885,541; c) the use of ultra-low input impedance preamplifiers to minimize mutual coupling between adjacent coils, such as described in U.S. Pat. No. 6,498,489; and d) the use of capacitive elements between adjacent coils to minimize mutual coupling between adjacent coils.